/* 
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 *     http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.harmony.javax.naming.spi;

import java.util.Hashtable;

import org.apache.harmony.javax.naming.Context;
import org.apache.harmony.javax.naming.Name;
import org.apache.harmony.javax.naming.NamingException;

/**
 * The <code>StateFactory</code> interface describes a factory used to get the
 * state of an object to be bound. Using a <code>lookup()</code> on a suitable
 * context, an class may be found representing, say, a printer; an
 * <code>ObjectFactory</code> may be used to create an instance of the printer
 * object class and methods defined by the printer class may be used to inspect
 * and manipulate the printer. There is a reverse mechanism in which a
 * <code>StateFactory</code> is used by the service provider to obtain the state
 * of the (in this case) printer for storing in the naming system. In addition
 * to implementing this interface, a <code>StateFactory</code> class must be
 * public and have a public constructor taking no parameters.
 * <p>
 * Note that while <code>StateFactory</code> is meant to be used in
 * <code>Context</code> service providers, whereas <code>DirStateFactory</code>
 * is meant to be used in <code>DirContext</code> service providers.
 * </p>
 */
public interface StateFactory {

	/**
	 * Returns a new instance of the specified object <code>o</code> containing
	 * the state of the object to be bound, customized by the specified
	 * <code>envmt</code> parameter. The name and context parameters optionally
	 * specify the name of the object being created.
	 * 
	 * Object and state factories are specified via environment properties from
	 * several sources including provider properties files (see the
	 * specification of the <code>Context</code> interface) and may comprise a
	 * list of factories. When the service provider looks to obtain the list of
	 * state factories, the environment and provider properties files are search
	 * for the property name specified by constant
	 * <code>Context.STATE_FACTORIES</code>. Each state factory in the resulting
	 * list is used by <code>NamingManager.getStateToBind()</code> which invokes
	 * this method on each of them until a non-null result is achieved or until
	 * the list is exhausted. If a <code>StateFactory</code> throws an
	 * exception, it should be passed back to the code that invoked
	 * <code>NamingManager.getStateToBind()</code> and no further state
	 * factories in the list are examined. An exception should only be thrown by
	 * a state factory if it is intended that no other state factories be
	 * examined. Usually, if an state factory is unable to return the state of
	 * an object, then null should be returned.
	 * 
	 * @param o
	 *            may be null, or specifies the returning instance
	 * @param n
	 *            may be null, or specifies the name relative to the specified
	 *            context <code>c</code>. The implementation may clone or copy
	 *            this object, but will not modify the original.
	 * @param c
	 *            the context to which the name parameter is relative, or may be
	 *            null when using a name relative the the default initial
	 *            context. If a factory uses this context object,
	 *            synchronization should be used as context objects are not
	 *            thread-safe.
	 * @param envmt
	 *            may be null; the implementation may clone or copy this object,
	 *            but will not modify the original.
	 * @return either a new instance of the specified object <code>o</code>
	 *         containing the state of the object to be bound, customized by the
	 *         specified <code>envmt</code> parameter. Or null if no object
	 *         could be created.
	 * @throws NamingException
	 *             if it is intended that no other state factories be examined.
	 */
	Object getStateToBind(Object o, Name n, Context c, Hashtable<?, ?> envmt)
			throws NamingException;

}
